1. Field of the Invention
The present invention relates to a technology for monitoring communication in an extended network wherein already existing communication apparatuses such as PDH communication apparatuses are each replaced by an SDH communication apparatus.
2. Description of the Related Art
In recent years, while the demand for improved reliability o f a communication network as a whole is getting even stronger, communication networks and communication lines supplied by different vendors as well communication lines implemented by a variety of media get connected to each other accompanying the progress of the integration of communication networks. For this reason, there is a demand for a monitoring system implemented for controlling the integrated communication network as a whole with a high degree of efficiency and an advanced technique. To put it concretely, by monitoring a variety of states in the communication network as monitored data, the occurrence of a failure can be inferred in advance, allowing a down state of the network to be avoided as one of advanced techniques to control the network.
As an example of implementation of a communication network to be integrated, a PDH (Plesiochronous Digital Hierarchy) communication network is known. The PDH communication network is a generic name of communication networks already existing prior to development of an SDH (Synchronous Digital Hierarchy) communication network which shows a remarkable growth in recent years. The SDH communication network is a new communication network constructed on the basis of a protocol which is standardized in conformity with recommendations made by the ITU-T and others.
That is, activities of integrating a PDH communication network constructed by using the conventional free (independent) protocol into an SDH communication network based on a new technology are intensified and, as a result, the demand for integration of a PDH monitoring system into an SDH monitoring system is rising. For this reason, it becomes necessary to transform the format of control signals generated by a PDH monitoring system implemented in an already existing PDH communication apparatus into a format that can be handled by an SDH monitoring system implemented in an SDH communication network without affecting the main signal network.